This invention relates to rotary switching apparatus for power transformers and specifically to de-energized rotary tap selecting switches. These switches are traditionally supplied for making minor adjustments to the primary winding ratio in order to compensate for line voltage variations related to physical distance from the point of power generation. Generally these adjustments are made at the time of installation and remain unchanged as long as the transformer remains at that site.
In known constructions, switches of the general class are immersed in transformer oil and are controlled from a single, externally mounted, operating mechanism coupled to them via a series of shafts and joints. In addition, the switches for each individual phase of the transformer are driven via additional couplings and shafts. When the operating mechanism travels through a fixed angular rotation to the next indicated tap position, the play in the plurality of joints can add up in a manner such that one or more of the switches may not complete the angular rotation necessary to make full engagement of the switch contacts. Depending upon the severity of the misalignment, there can be overheating or arcing both of which can cause catistrophic failure of the transformer.
The rotatable bridging devices customarily found in such switches are constructed in such a manner as to provide adequate contact area, mechanical and magnetic clamping forces and the ability for self-alignment due to wear in the contacts. The drawback of such mechanisms previously encountered is due to their complexity and the use of many accurately machined pieces required to obtain the desired attributes of a reliable contact assembly. Such construction is prohibitive in a low volume market where machining, inventory and labor costs must be carefully considered.